1. Field of the Invention
The present invention relates to a cold cathode fluorescent lamp (CCFL) assembly, and to an inverter-type drive circuit thereof.
2. Description of the Related Art
A liquid crystal display (LCD) uses a CCFL as a backlight source. The CCFL is typically driven by an inverter-type drive circuit.
Referring to FIG. 1, a CCFL assembly disclosed in Taiwanese Patent Publication No. 521947 is shown to include an inverter-type drive circuit 1. The inverter-type drive circuit 1 is controlled by a power supply module 20 to drive CCFLs 21, 22, which are coupled to the inverter-type drive circuit 1 and further coupled in parallel to each other. The inverter-type drive circuit 1 includes a transformer 12, and a push-pull drive circuit 11 having a pair of transistors (Q1, Q2) and a capacitor (C1). A primary winding of the transformer 12 includes an excitation coil (Lm) and a drive control coil (Ld). The excitation coil (Lm) is center-tapped and coupled to the power supply module 20. The transistors (Q1, Q2) have collectors coupled to the excitation coil (Lm), bases coupled to the drive control coil (Ld) , and grounded emitters. One terminal of a secondary winding of the transformer 12 is connected to the CCFLs 21, 22 respectively through high voltage capacitors (C2, C3).
During operation of the inverter-type drive circuit 1, the drive control coil (Ld) alternately drives the transistors (Q1, Q2) to conduct to thereby excite the excitation coil (Lm). This results in the transfer of power from the excitation coil (Lm) to the secondary winding, thereby activating the CCFLs 21, 22.
However, since impedances of the CCFLs 21, 22 may not be identical, currents passing through the parallel-connected CCFLs 21, 22 may differ. This may result in different brightness levels between the CCFLs 21, 22. Therefore, a balance transformer 13 is coupled between one terminal of each of the CCFLs 21, 22 and one terminal of the secondary winding of the transformer 12. While the balance transformer 13 ensures that the currents flowing to the CCFLs 21, 22 are uniform, circuit complexity and size are increased.
In addition, since the inverter-type drive circuit 1 is able to drive a maximum of only two of the CCFLs 21, 22, more of the inverter-type drive circuits 1 are required if it is desired to operate additional CCFLs. This further increases circuit complexity and takes up significant space.
FIG. 2 shows a CCFL assembly including an inverter-type drive circuit 6 disclosed in U.S. Pat. No. 5,495,405. A primary-side circuit 61 of the drive circuit 6 is capable of driving only a single transformer. In a secondary-side circuit 62 of the drive circuit 6, there is provided an additional inductor 63, and a high voltage capacitor 64 and a CCFL 65 are connected in parallel. Only the single CCFL 65 may be driven with this configuration such that when it is desired to drive additional lamps, it is necessary to use a corresponding number of the drive circuits 6. Hence, the same problems of increased circuit complexity and significant use of space are encountered with this prior art structure.